doubling

[second strike]

just put a new grendel togrther with a high end 2 stage,first time firing it doubled and will also triple on occasion..swapped bcg with another proven grendel,,no help..swapped lowers and problem is
gone..both work well...thoughts?? appreciate any constructive comments..regards,,Rich [it doesn't double every round,,4th 5th and so on]

[WildBill3/75]

more info;
m16 or ar15 carrier?
Buffer spring?
Buffer?

I've been getting a double fire too every once in a while but I think my problem is due to an exceptionally heavy buffer+tubb flatwire. I have yet to test after reducing the buffer weight but I think this combo was my cause.

The m16/ar15 uses a free floating firing pin. If you have a heavy enough mass moving at just the right speeds I believe it would be enough to ignite a primer.

Edit---Could also be that the trigger isn't setup correctly, what trigger are you running?

[second strike]

appreciate the reply WB,,i use m16 carrier in all my builds..everything else depends..the part where i swap lowers and all is well is the dilema..

[WildBill3/75]

No problem, I see 3 variables that could be the source of your problem.

Buffer spring
Buffer weight
trigger

Depending if they are both rifle length buffers or m4 buffers. I'd swap the buffer+buffer spring from the good lower and try it in the "bad lower" and if you still got an issue it is the trigger.

Also, have you function checked the trigger?. https://www.youtube.com/watch?v=IclDr_qUgbc

[mongoosesnipe]

Chances are it is you who is doubling, in many cases those new to the super short resent and light wieght of a high end 2 stage match trigger can often accidently bump fire or double fire the trigger and I have heard stories of accidental mag dumps when people don't have the trigger set up properly and pull the trigger wrong...

[second strike]

that's not the problem,,i'm right back to when i switch lowers they both work fine.i've used 2 stage in the last 10-12 i've built with no issues.

[terrywick4]

I would be concerned that the disconnector isn't timed properly. I had a Jewell trigger in my grendel and I couldn't get it not to double tap, put in a JP trigger and works great now.

[pds]

My money's on a trigger problem!

pds

[mongoosesnipe]

that's not the problem,,i'm right back to when i switch lowers they both work fine.i've used 2 stage in the last 10-12 i've built with no issues.

Work fine with 556 or is this a new trigger that is giving you problems the Grendel has more recoil and could be causing you to bump

[second strike]

appreciate the replys but they still don't adress the issue...WHEN I SWITCH LOWERS BOTH RIFLES WORK FINE ..both are the same,,buffer,spring,,trigger and on and on..question is why does one double and the other doesn't...both are grendels as i said in the beginning..

[montana]

It is probably one of two problems. I have an M1A1 with a very light two stage trigger and it will seem to double tap if I let it recoil too much, similar to what happens using a slide fire stock. Two, your dis connect is not properly working and you have a problem that needs to be corrected with your trigger assembly. I have had standard triggers on AR rifles double tap. I filed the bottom of the disconnect so it has more room to grab and my problem was solved . This is what to do on a standard trigger but you should be able to check your trigger to see if it is functioning correctly in the same manner. If your two stage trigger is an not functioning I would send it back to the manufacturer.

You will first separate the upper from the lower (std warning--> be sure the firearm is unloaded/safe)

Hold trigger to rear, bring hammer back and catch hammer via disconnect... slowly release trigger... did hammer trade off to trigger and stay, or did it drop?

If it dropped, remove the trigger and disconnect, look at the disconnect spring anyway, as a few people have installed them backward and had similar problem.

See where the disconnect leg sits on the trigger, file the bottom of the disconnect leg so it will tip and grab the hammer shelf a bit deeper, don't need much though, re-test.

Ideally, the shelf on the hammer will pass the disconnect hook so close so as not to hit, and not see any visible air gap (finger off trigger)

I would also switch uppers and check to see if your trigger is being bumped because of variation in upper receiver tolerances making your disconnect fail.

[IceAxe]

I wonder if it could be a slam fire? Try switching firing pins.

[NugginFutz]

appreciate the replys but they still don't adress the issue...WHEN I SWITCH LOWERS BOTH RIFLES WORK FINE ..both are the same,,buffer,spring,,trigger and on and on..question is why does one double and the other doesn't...both are grendels as i said in the beginning..

Ok. As I understand you, both rifles have a configuration where they behave with no issues. It is when one of the uppers is paired with a specific lower that the doubling occurs. Correct?

If that is the case, and swapping the uppers resolves it, I'd try switching just the BCG's, next, and see if the problem moves. If that doesn't change things, it is the upper / lower combo.

Are both barrels the same? 16" 18", etc?

Gas Systems: Carbine, Mid Length or Rifle Length?

You mention that the internals are the same between both lowers, but have you inspected / function checked the problem lower?

Just to restate it,

1. Install your upper, remove any magazine, and ensure the chamber is clear.
2. With the hammer cocked, turn off safety. Press the trigger and release. The hammer should fall.
3. Re-cock the hammer using the charging handle. It should stay cocked.
4. With the safety on, press the trigger. The hammer should NOT fall. If it does, your safety is fubar'd.
5. Turn the safety off. Press the trigger, but do not release. The hammer should fall.
6. While continuing to press the trigger, re-cock with the charging handle and let it slam forward on its own (don't ride it down). The hammer should remain cocked. If it falls, you have an issue with the hammer disconnector engagement.

Since your issue is intermittent, these steps (especially through #6) should be repeated several times.

If the trigger group is properly installed (visually confirmed) and the function check does not reveal any problems, that would leave the gas system (hard cycling) as another possibility. Is your brass showing signs of extreme duress? Ejector swiping?

[second strike]

problem corrected

sent trigger assy. back to mfg.,,turned out to be disconnector ,,worked fine during function test,,not so when actually firing..good to go now...